Daniel Weidinger1, Cassidy Houchins2 and Jeffrey C. Owrutsky3
(1) National Research Council Postdoctoral Researcher
(2) SRA International
(3) Chemistry Division, Naval Research Laboratory, Washington, DC
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OSU International Symposium on Molecular Spectroscopy June 23, 2011
Vibrational Dynamics of Tricyanomethanide
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Tricyanomethanide Infrared Spectroscopy
A. Why study tricyanomethanide (TCM)?• Ionic liquids for fuel cells, solar cells
• Similar to anion N(CN)2- (DCA)
low viscosity → high conductivity
B. Vibrational probes and solvation probes• Anion studies: NCO-, N3
-, N(CN)2-, NCS-
• TCM hydrophilic & strong IR absorber
C. Metal cyanides • Contrast with metal cyanides, e.g. Au(CN)2
-
• Prussian blue and CN adsorbates
D. New research• Steady state and dynamic spectra
• Ab initio calculations
Source: http://www.ensem.inpl-nancy.fr/
Source: http://www.chem.monash.edu.au
D. Weidinger et al., J. Chem. Phys. 134 (2011) 124510
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Tricyanomethanide Vibrations
• IR-active frequencies around 2170 cm-1
• Asymmetric CN-stretch (E’)• High Intensity (~50,000 M-1cm-2)
Raman Shift (cm-1)
2200 2220 2240 2260
Inte
nsity
(to
tal c
ount
s)
3.7e+5
3.8e+5
3.8e+5
3.9e+5
3.9e+5
4.0e+5
4.0e+5
TCM Raman Spectrum (solid KTCM)
TCM Vibrational Modes (D3h symmetry)
• Raman A’ band at 2222 cm-1; previous spectra:• Beaumont et al., Inorg. Chim. Acta 84 (1984) 141• Hipps et al., J. Phys. Chem. 89 (1985) 5459• Dixon et al., J. Am. Chem. Soc. 108 (1986) 2582
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Tricyanomethanide IR Spectra
Vibrational Band FrequenciesTCM Spectra
1 Dahl et al., J. Chem. Phys. 123 (2005) 0845042 Dixon et al., J. Am. Chem. Soc. 108 (1986) 2582
TCMCenter Freq.(cm-1)
DCA Center Freq.(cm-1)
NCS- Center Freq.(cm-1)
H2O 2172.0 2151.91 2164.01
D2O 2171.5 2149.41 2163.31
Methanol 2172.3 2147.81 2157.01
Formamide 2167.1 2141.91 2158.71
[BMIM][BF4] 2162.4 2131.01 2057.11
Solid 21622 -- --
DMSO 2161.7 2128.21 2055.81
Frequency (cm-1)
212021602200
No
rma
lize
d A
bso
rba
nce
(a
rb. u
nits
)
H2O
D2O
Methanol
DMSO
BMIM
Formamide
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IR Pump-Probe – Vibrational Relaxation
ν = 0
2
1
Transient Absorption
Transient Bleach
Frequency
Ab
sorp
tio
n
Pump-probe diagramUltrafast Pump-Probe IR setup:
•4 μJ, ~350 fs IR pulses
•5 cm-1 resolution
Ti:Sapphire Oscillator
Regenerative Amplifier
OPA
DFG Crystal
Sample
Monochromator
Delay Stage
IR Detector
To Lock-in,
Computer
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IR Pump-Probe – Vibrational Relaxation
Frequency (cm-1)
2120214021602180
Abs
orba
nce
Cha
nge
(mO
D)
-40
-20
0
20
40
• Strong transient absorption (as much as 40 mOD with 1 uJ pump)
• Concentrations of ~0.1 M
• Similar widths, decay times from adsorption, bleach features
• FWHM = 10 cm-1
• Anharmonicities of ~16 cm-1
Transient Spectrum:
TCM in DMSO, 1 ps Delay
Time (ps)
0 20 40 60 80
Ab
sorb
an
ce C
ha
nge
(m
OD
)
0.0
0.2
0.4
0.6
0.8
1.0
H2O FA BMIM
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IR Pump-Probe – Vibrational Relaxation
• Slower vibrational relaxation than DCA, N3
-
• Relaxation in MeOH slower than H2O, opposite of frequency trend
TCM TA Lifetime
(ps)
TCM TB Lifetime
(ps)
DCA T1
(ps)NCS- T1
(ps)
H2O 4.8 5.2 1.9 2.5
D2O 12.2 12.7 2.9 21.3
Methanol 12.0 17.8 4.7 22.6
Formamide 18.1 18.1 4.6 21.5
[BMIM][BF4] 27.5 33.0 8.4 63.1
DMSO 28.1 36.8 11.0 77.0
TCM TA Decay
• Decay lifetimes vary from 5 to 30 ps
• Solvent trend is similar to DCA & most small anions
Table of VER lifetimes
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Calculations of CN bands
Calculated TCM Frequencies
Model / Basis Set Symmetric Anti-Symmetric
νcnS
cm-1
IR Intensity
km / mole
νcnAS,1
cm-1
IR
Intensity
km / mole
MP2/aug-cc-pVDZ 2137.2 -- 2146.7 370
B3LYP/aug-cc-pVDZ 2282.5 -- 2230.9 481
B3LYP/aug-cc-pVTZ 2292.0 -- 2238.1 483
Experimental 2222 -- 2170 --
• Calculations performed using Gaussian 09
• Structures optimized within the C1 point group
• Frequencies calculated for all optimized structures to ensure minimum
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Calculations of CN bands
Experimental and Calculated TCM and DCA Frequencies
Model DCA1 TCM
νcnS
cm-1
νcnAS,1
cm-1
νcnS
cm-1
νcnAS,1
cm-1
MP2 2183 2199 2137 2147
B3LYP 2209 2186 2282 2238
Experiment 2232 2179 2292 2170
• MP2 calculations for DCA and TCM have same reversed energy order
• Order is correct in B3LYP calculations
1 Georgieva et al.., J. Mol. Struct. 752 (2005) 14
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Calculations of Thermochemistry
• Electron affinities:
• Structures optimized at
MP2/aug-cc-pVDZ and
B3LYP/aug-cc-pVXZ (x=2,3)
• Proton Affinity calculated from
MP2 and B3LYP optimized
structures
• Pertinent to transport properties &
electrolytic applications1,2
Model VDE
(eV)
ADE
(eV)
PA
(eV)
MP2/aug-cc-pVDZ 3.8 4.3 13.3
B3LYP/aug-cc-pVDZ 4.0 4.0 13.0
B3LYP/aug-cc-pVTZ 4.0 4.0 13.1
Calculated electron detachment energies and proton affinities (TCM)
1 S. Y. Kim et al., Nature Communications 1 (2010)2 Q. Dai et al., Comptes Rendus Chimie 9 (2006) 6013 B. Jagoda-Cwiklik et al., J. Phys. Chem. A 111 (2007) 7719
• Observed3 DCA electron affinity
(ADE) = 4.135 eV
• Calculated DCA ADE (by MP2) is
4.1 eV
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Conclusions
• IR Spectroscopy and IR Pump-Probe Studies of TCM
• “New” IR solvent probe
• High frequency
• Strong CN stretch
• Good solubility
• Shift-lifetime trend similar to DCA
• Long decay time for CN-containing anion
• MeOH is anomalous solvent
• Computations
• IR and Raman frequencies
• Electron Affinities
• Proton Affinities and transport properties
Acknowledgements
• Scientists• Jeffrey C. Owrutsky (NRL)• Cassidy Houchins (SRA International)• Code 6111
• Funding:
Office of Naval Research
• Sponsorship:
National Research Council
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Extras
TCM TA Lifetime
(ps)
TCM TB Lifetime
(ps)
DCA T1
(ps)NCS- T1
(ps)
H2O 4.8 ± 0.4
5.2 ± 0.4
D2O 12.2 ± 0.6
12.7 ± 0.4
Methanol 12.0 ± 1.9
17.8 ± 1.7 4.7 ± 0.5
22.6 ± 2.1
Formamide
18.1 ± 2.9
18.1 ± 0.4
[BMIM][BF4]
27.5 ± 4.0
33.0 ± 9.5 8.4 ± 0.7
63.1 ± 3.1
DMSO 28.1 ± 2.9
36.8 ± 4.6 11.0 ± 4.9
77.0 ± 5.6
Model / Basis Set
Symmetric Anti-symmetric
νcnS
cm-1
IR Intensity
km / mole
νcnA
S,1
cm-1
IR
Intensity
km / mole
νcnAS,
2
cm-1
IR
Intensity
km / mole
MP2/aug-cc-pVDZ
2137.2
-- 2146.7
370 2146.8
370
B3LYP/aug-cc-pVDZ
2282.5
-- 2230.9
481 2231.0
481
B3LYP/aug-cc-pVTZ
2292.0
-- 2238.1
483 2238.1
483